IN-VIVO MICRODIALYSIS OF 5-HYDROXYINDOLEACETIC ACID AND GLUTAMIC-ACIDIN THE HAMSTER SUPRACHIASMATIC NUCLEI

The technique of in vivo brain microdialysis rapidly is becoming a pop ular tool for research on the neurochemical basis of physiological and behavioral functions. The present study describes the application of microdialysis to investigate the endogenous release of 5-hydroxyindole acetic acid (5-HIAA) and glutamic acid in the suprachiasmatic nuclei ( SCN) of hamsters. There were apparent circadian patterns of release of both of these neurosecretions, with peak levels occurring during the dark phase. Pharmacological manipulations of serotonin release and reu ptake, using tetrodotoxin and citalopram, respectively, provided evide nce that the nocturnal increase in 5-HIAA reflects an increase in sero tonergic synaptic activity, rather than intraneuronal metabolism of un released serotonin. These results illustrate the usefulness of the mic rodialysis technique for studies on the neurochemistry of central pace maker function.